The below selected organic peroxides are unstable and thermally sensitive compounds, i.e. compounds that decompose under the effect of temperature, because of the presence of the oxygen-oxygen bond which can open within an energy range ΔH of from approximately 84 to 184 kJ/mol, depending on the nature of the organic peroxide.
Thermally sensitive organic compounds, such as the below selected organic peroxides according to the invention, result in the formation of radicals by thermal decomposition. Advantage is taken of this decomposition in order to use these compounds as free-radical reaction initiators, but it needs to be perfectly controlled during the manufacture of these compounds.
Thus, the synthesis of the below selected organic peroxides requires very important precautions in order to prevent any accident in the industrial processes used. Generally, open reactors are used, making it possible in this way to compensate for any runaway of the reaction without the product being contained, which would lead to irreparable damage (Encyclopaedia of Chemical Technology—Kirk-Othmer—Fourth Edition, Vol. 187, 1996, pages 292 to 293).
Moreover, in batch processes, all the reactants are initially loaded into the reactor, this type of process generally being used for the completely safe production of moderate amounts of compounds.
When greater production volumes are required, continuous processes are carried out. In continuous processes, the starting materials are continuously introduced into a reaction zone and kept in this zone for the required reaction period. The presence, at each moment, of a small amount of unstable compounds in the reaction mass makes continuous processes safer than batch processes, while at the same time providing greater productivity and higher purity for the products obtained.
Mention may, for example, be made of U.S. Pat. No. 4,075,236, which describes a process and a device for the continuous preparation of very pure peroxyesters with a high throughput. This process uses two open reaction zones in series comprising stirring devices which intimately mix the reactants, and cooling devices which dissipate the reaction heat. The cooled reaction mixture leaving the reactor is then continuously introduced into a separating device. The products are obtained with a yield of greater than 90% and have a purity of greater than 99%.
U.S. Pat. No. 3,950,375 describes a process for the continuous preparation of peroxydicarbonates, also using two stirred and cooled open reactors in series, the reaction product then being isolated by centrifugation. The products are obtained with a purity of greater than 99% and the productivities, expressed by parts by weight (kg) and per hour, are of the order of 50.
In these processes of the prior art, the reactors nevertheless contain a large volume of organic peroxide-based reaction mixture, which can lead to risks of a possible exothermic reaction such as a decomposition, despite the presence of a device for dissipating the reaction heat. Moreover, the mechanical stirrers conventionally used may not provide optimal mixing of the reaction phases, all the more so since these phases are generally immiscible.
These disadvantages of prior art are resolved by carrying out, according to the invention, the synthesis of the below selected organic peroxides using a closed plate exchanger running as micro-reactor or mini-reactor technology.
By using such technology, it is now possible to drastically reduce the reaction volume and to very precisely control the temperature of the reaction medium so as to satisfy the elementary criteria of safety, while at the same time improving the productivity of the plant. The quality of mixing is very important, since very rapid and very effective mixing of the reactants all along the reactor makes it possible to achieve very short periods of time spent by the reactants in the reactor and makes it possible to carry out reactions in a few seconds, even when the mixtures are two-phase mixtures. As a result, by use of micro-reactors or mini-reactors only small volumes of reaction mixture based on the below selected organic peroxides will limit the risks associated with a possible exothermic reaction such as a decomposition. Moreover, a good heat exchange, expressed as exchange surface relative to reaction volume, makes it possible to control and master more successfully the possible decomposition reactions of these compounds.
These essential advantages result in an improvement in the safety of the industrial processes for the synthesis of the below selected organic peroxides.
The micro-reactor or mini-reactor technology is based on a system of miniaturized reactors, of mixers, of heat exchangers and other elements with structures on a scale that can range from a micrometer to a millimeter.
To use a process in a closed reactor is one of the advantages of micro-reactor or mini-reactor technologies. Micro-reactors and mini-reactors can operate continuous by use of miniaturized tube reactors having small size channels. Moreover, because of the reduced size of the channels and thus high surface-to-volume ratios, they will be much more efficient than conventional batch reactors, in terms of mass and heat transfer. This technology is particularly suitable for the completely safe synthesis of the below selected dangerous organic peroxides of the invention.
The article entitled “Novel Liquid Phase Microreactors for Safe Production of Hazardous Specialty Chemicals” in Microreact. Technol. Ind. Prospects, Proc. Int. Conf. 3rd, 171-180 (1999), presents the advantage of microreactors in relation to the possibility of producing reactors with small channels that can be produced by microfabrication techniques. That article describes a microreactor which comprises two groups of five microchannels corresponding to elementary flow rates of the two reactants which are remixed in a tube online. The microreactor may comprise a heat exchange device and temperature detectors. A mixing time of 10 ms and a heat transfer coefficient of 1445 W/m2° C. are obtained and the reactor is shown to operate with 11 psi pressure drop at the 1.0 ml/min design flow rate. Such a microreactor presents the disadvantage of not enabling extrapolation to an industrial scale, the production volume for a single microreactor being only about 1000 lbs/yr. To expand the production capacity, it is necessary to scale out with a great number of microreactors used in parallel. This disadvantage is resolved by using, according to the present invention, a single microreactor with considerably higher flow that may consist of a large number of plates defining between them reaction chambers connected in series.
The publications Chem. Eng. Technol. 2005, 28, 3, pp. 276-284 and Organic Process Research & Development, 2002, 6, pp. 187-189 make reference to preparations, in a microstructured reactor, of cyclic peroxides such as ascaridole from α-terpinene and singlet oxygen generated by irradiation.
Document DE 10257239 describes the continuous photo-oxidation of olefins in microreactors, in the presence of light and oxygen, so as to prepare organic intermediates such as, for example, allyl hydroperoxides, 1,2-dioxetanes or endoperoxides. In this case, it is not a liquid-liquid reaction.
Application WO 04/091771 describes a microreactor that is particularly suitable for the preparation of hydrogen peroxide by reaction of hydrogen and oxygen. This microreactor is composed of plates and comprises a reaction zone included between the plates. These plates can optionally contain a catalyst and allow the reaction exothermicity to be dissipated. The spacing between the plates, called slot, is less than 1500 micrometers in size. Gas-phase heterogeneous reactions are advantageously carried out in these devices.
Document EP 1 313 554 relates to a process for carrying out reactions between at least two reactive fluids, using a reactor having spaces between two plates in the form of slots. The reactions carried out are exothermic or endothermic reactions between several reactants, in the presence or absence of catalyst. The process is particularly suitable for heterogeneous reactions in the presence of a granular catalyst placed either in the reaction spaces, or on the lateral surfaces of the wall elements which are turned towards the reaction spaces. This process is used for the direct synthesis of hydrogen peroxide in the gas phase, for the preparation of propenal or of acrylic acid from propene, or the production of ethylene oxide or of propylene oxide.
In addition, in WO 02/085511, a plate exchanger is disclosed for exchange and/or reaction between at least two fluids. Inlet nozzles may be considered to enable inlets of one or several reactants in the reaction chamber. Endothermic or exothermic reactions can be carried out in these plate exchangers. However, this document neither discloses nor suggests to use such an exchanger for a process for synthesis the below selected organic peroxides.
An industrial process suitable for the synthesis of the below selected organic peroxides using a close plate exchanger running as microreactor or minireactor technology, that limits their decomposition and that provides a high degree of industrial safety, with high yields and high degrees of purity, has now been discovered.
This process can be carried out advantageously as an ex-situ process, i.e. on the site where free-radical cross-linkings or polymerizations are carried out in the presence of an organic peroxide selected from the group consisting of di(n-propyl)peroxydicarbonate of CAS Reg. No. 16066-38-9, di(sec-butyl)peroxydicarbonate of CAS Reg. No. 19910-65-7, di(2-ethylhexyl)peroxydicarbonate of CAS Reg. No. 16111-62-9, 1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate of CAS Reg. No. 95718-78-8, α-cumyl peroxyneodecanoate of CAS Reg. No. 26748-47-0, α-cumyl peroxyneoheptanoate of CAS Reg. No. 104852-44-0, tert-amyl peroxyneodecanoate of CAS Reg. No. 68299-16-1, tert-butyl peroxyneodecanoate of CAS Reg. No. 26748-41-4, tert-amyl peroxypivalate of CAS Reg. No. 29240-17-3, tert-butyl peroxypivalate of CAS Reg. No. 927-07-1, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane of CAS Reg. No. 13052-09-0, tert-amyl peroxy-2-ethylhexanoate of CAS Reg. No. 686-31-7, tert-butyl peroxy-2-ethylhexanoate of CAS Reg. No. 3006-82-4, tert-amyl peroxyacetate of CAS Reg. No. 690-83-5, tert-butyl peroxyacetate of CAS Reg. No. 107-71-1, tert-amyl perbenzoate of CAS Reg. No. 4511-39-1, tert-butyl perbenzoate of CAS Reg. No. 614-45-9, OO-tert-amyl-O(2-ethylhexyl)monoperoxycarbonate of CAS Reg. No. 70833-40-8, OO-tert-butyl-O-isopropyl monoperoxy-carbonate of CAS Reg. No. 2372-21-6, OO-tert-butyl 1-(2-ethylhexyl)monoperoxy-carbonate of CAS Reg. No. 34443-12-4, poly(tert-butyl peroxycarbonate)polyether of CAS Reg. No. 100-41-4, decanoyl peroxide of CAS Reg. No. 762-12-9, lauroyl peroxide of CAS Reg. No. 105-74-8, succinic acid peroxide of CAS Reg. No. 123-23-9, benzoyl peroxide of CAS Reg. No. 94-36-0, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane of CAS Reg. No. 6731-36-8,1,1-di(tert-butylperoxy)cyclohexane of CAS Reg. No. 3006-86-8, 1,1-di(tert-amylperoxy)cyclohexane of CAS Reg. No. 15667-10-4, n-butyl 4,4-di(tert-butylperoxy)valerate of CAS Reg. No. 995-33-5, ethyl 3,3-di(tert-amylperoxy)butyrate of CAS Reg. No. 67567-23-1, tert-butyl peroctoate of CAS Reg. No. 3006-82-4, ethyl 3,3-di(tert-butylperoxy)butyrate of CAS Reg. No. 55794-20-2, cumene hydroperoxide of CAS Reg. No. 80-15-9, and tert-butyl hydroperoxide of CAS Reg. No. 75-91-2, said organic peroxide being used directly just after it has been produced in the polymerization or cross-linking reactor, more particularly introduced continuously in the course of the polymerization or cross-linking reaction.